Thermal conditioning provides heating, air exchange, and cooled (dehumidified) air within a building to maintain an interior temperature and air quality appropriate to the comfort and other needs or goals of the occupants. Thermal conditioning may be provided through a centralized forced air, ducted heating, ventilating, and air conditioning (HVAC) system, through discrete components, such as electric baseboard heaters for heat, ceiling or area fans for air circulation, and window air conditioners for cooling, heat pumps for heating and cooling, or through a combination of thermal conditioning devices. However, for clarity herein, all forms of thermal conditioning equipment, whether a single do-all installed system or individual contributors, will be termed HVAC systems, unless specifically noted otherwise.
The types of thermal conditioning that are required inside of a building, whether heating, ventilating, or cooling, are largely dictated by the climate of the region in which the building is located and the season of the year. In some regions, like Hawaii, air conditioning might be used year round, if at all, while in other regions, such as the Pacific Northwest, moderate summer temperatures may obviate the need for air conditioning and heating may be necessary only during the winter months. Nevertheless, with every type of thermal conditioning, the costs of seasonal energy or fuel consumption are directly tied to the building's thermal efficiency. For instance, a poorly insulated building with significant sealing problems will require more overall HVAC usage to maintain a desired inside temperature than would a comparably-sized but well-insulated and sealed structure. As well, HVAC system efficiency, heating and cooling season duration, differences between indoor and outdoor temperatures, and internal temperature gains attributable to heat created by internal sources can further influence seasonal fuel consumption in addition to a building's thermal efficiency.
Forecasting seasonal fuel consumption for indoor thermal conditioning, as well as changes to the fuel usage rate triggered by proposed investments in the building or thermal conditioning equipment, must take into account the foregoing parameters. While the latter parameters are typically obtainable by the average consumer, quantifying a building's thermal conductivity remains a non-trivial task. Often, gauging thermal conductivity requires a formal energy audit of building exterior surfaces and their materials' thermal insulating properties, or undertaking empirical testing of the building envelope's heat loss and gain.
Once the building's thermal conductivity (UATotal) and the accompanying parameters are known, seasonal fuel consumption can be estimated. For instance, a time series modelling approach can be used to forecast fuel consumption for heating and cooling, such as described in commonly-assigned U.S. patent application, entitled “Computer-Implemented System And Method For Modeling Building Heating Energy Consumption,” Ser. No. 14/631,798, filed Feb. 25, 2015, pending, the disclosure of which is incorporated by reference. In one such approach, the concept of balance point thermal conductivity replaces balance point temperature and solar savings fraction, and the resulting estimate of fuel consumption reflects a separation of thermal conductivity into internal heating gains and auxiliary heating. In a second approach, three building-specific parameters are first empirically derived through short-duration testing, after which those three parameters are used to simulate a time series of indoor building temperatures and fuel consumption. While both approaches usefully predict seasonal fuel consumption, as time series-focused models, neither lends itself well to comparative and intuitive visualizations of seasonal fuel consumption and of the effects of proposed changes to thermal conditioning components or properties.
Alternatively, heating season fuel consumption can be determined using the Heating Degree Day (HDD) approach, which derives fuel consumption for heating needs from measurements of outside air temperature for a given structure at a specific location. An analogous Cooling Degree Day (CDD) approach exists for deriving seasonal fuel consumption for cooling. Although widely used, the HDD approach has three notable limitations. First, the HDD approach incorrectly assumes that heating season fuel consumption is linear with outside temperature. Second, the HDD approach often neglects the effect of thermal insulation on a building's balance point temperature, which is the indoor temperature at which heat gained from internal sources equals heat lost through the building's envelope. In practice, heavily insulated buildings have a lower balance point temperature than is typically assumed by the HDD approach. Third, required heating (or cooling) depends upon factors other than outdoor temperature alone, one factor of which is the amount of solar radiation reaching the interior of a building. In addition to these three procedural weaknesses, the HDD approach fails to separate input assumptions from weather data, nor is intuitive to the average consumer. (For clarity, the Heating Degree Day and Cooling Degree Day approaches will simply be called the Degree Day approach, unless indicated to the contrary.)
Therefore, a need remains for a practical and comprehendible model for predicting a building's seasonal fuel consumption that is readily visualizable.
A further need remains for a practical and comprehendible model for predicting changes to a building's seasonal fuel consumption in light of possible changes to the building's thermal envelope or thermal conditioning componentry.